Control system



Sept. 20, 1949. G. E. KING 2,482,492

CONTROL SYSTEM Original Filed Nov. 16, 1944 WITNESSES: :3

. INVENTOR fl/ ge E. Kin

BY Ms, W

ATTORNEY Patented Sept. 20, 1949 UNITED STAT ES PATENT OFFICE.

CONTROL SYSTEM George-E. King, Pittsburgh, Pa., assignorto Westinghouse Electric Corporation, East, Pittsburgh, Pa., a corporation of Pennsylvania,

7' Claims.

This invention relates. generally, to constant current electric drives and, more particularly, to a constant. current electric drive which embodies a plurality ofdriving motors in which the armature currents of the motors. are maintained at a constant value. by means of a specially designed generator or a generator with, a constant current regulator.

This application is: a division of my copending application Serial No. 563,754, filed November 16, 1944, entitled Control systems, now United States Patent 2,438,010, granted March 16, 1948, and assigned to the Westin house Electric Corporation.

The invention as hereinafter disclosed is particularly adapted for operating; a number of motors which drive sugar centriiugals. However, it will be understood thatthe invention may be, utilized otherwise, for example, in cargo winches, towing winches, etc.

With constant current systems used to drive a motor of sugar centrifugal motors, it. is possible to operate these. motors such that some may be starting, some, running... and some braking at the same instant of time. Thus, the motors which are braking may regenerate into. the constant current system, and provide additional. energy for operating the motors, which are ac-. celerating without producing an. additional burden upon the constant current generator. systems of control, hereinafter disclosed, in general, provide constant, torque acceleration and braking of the motors. with provision, for operating the motors at any selected speed within the capacity of the. system and maintaining this speed constant once the, motor has accelerated to the desired speed.

A principal. object of this invention is to provide an electric. drive which is simple in its elements and in. its operation.

Another object of this invention is to provide an electric drive which includes, provisions for obtaining constant torque, acceleration, and braking of. the motor.

Still another object of the invention s. to provide an electric drive in, which certain electrical, characteristics of. the motor are utilized to effect a control. of the motor.

A further object of the invention is to provide an electric drive which includes provisions for obtaining constant torque acceleration and brakingof the motor and constant speed regulation at, a selected motor speed.

Other objects and advantages will become apparent from a study of the following disclosure The . 2 when considered in'coniunction. with the accompanyingv drawings, in which:

Figure 1v schematically illustrates a constant current electric drive embodying the fundamental principles. of this invention;

Fig. 2v is a modification of the invention. illustrated. in Fig. 1;,

Fig. 3 graphically illustrates. the.v operating characteristics df the control generator illustrated inFigs, land 2.

Referring. now to Fig, 1 of the drawings, the electric drive illustrated therein comprises, generally, a groupof drive motors designated as IM to, 3M, inclusive, a. constant current generator- IG for energizing the armature windings of the drive motors, a constant .voltage generator 261 for supplying a constant voltage to certain elements of the control system and a prime mover PM for driving the. generators. So much of the drive, is common to these motors. Additional control elements for the motor IM are bracketed in the. dot-dash outline and designated generally IMC.. Similar control elements for the motors 2M and 3M are. comprised in the blocks 2M0 and tailed.

The control elements llVIC include a control generator Q driven by prime mover PM for regulating the. motor field winding IMF, and a pilot generator PG driven by the drive motor IM.

far described and generally designated IMC are utilized only to. control the operation. of the driving motor IM. As, previously noted the, control elements for the. driving motors. 2M and 3M are. respectively designated ZMC and 3M0, and for the purpose of simplifying the illustration of, this. invention are shown only in block diagram. It will be understood in this connection. that the. control systems ZMC and 3M0 include operating elements such as those indicated in iMC. The p ime mover PM, however, may be utilized to drive the control generator such as C of each or these systems.

The balance of the description relating to- Fig. 1 Will be described in connection with the control system relating to drive motor IM. In this 3 connection, the function of the control system EMS and 3M0 will be understood.

The armature winding of the motor IN! is connected in a series loop with the armature winding of the constant current generator IG and a starting resistor IR is connected in this series loop. The constant current generator may be any suitable type, since, per se, it forms no part of this invention. As illustrated, it is provided with a single field winding IGF which is controlled by the output of the Regulator so designated in the drawings. This Regulator for the operating characteristics desired will so regulate the excitation of the single field winding that the armature currents will be maintained at a constant level for any loading or speed of operation of the motor IM. The single field winding IMF for the drive motor is connected in a series loop with the series field CSF for the control generator C, the armature winding thereof and the adjustable resistor TR. It is thus energized according to the electrical output of the control generator 0. The control generator C has special operating characteristics which will hereinafter be noted in detail. In addition to the series field winding CSF, the control generator is provided with a pattern field winding CPF which is energized according to the electrical output of the constant voltage generator, designated 2G. The excitation of this pattern field Winding may be varied according to the setting of the adjustable resistor ARI connected in series therewith to obtain variable operating characteristics of the motor. A voltage field winding CVF is also provided and is differential y connected with respect to the field winding CPF. The voltage field winding is adjustably energized depending upon the setting of the adjustable resistor ARZ, by the output of the pilot generator PG which is mechanically driven by the drive motor IM. The single field winding PGF for the pilot generator is enerized according to the electrical output of the constant voltage generator 26. Since the field excitation of the pilot generator is a constant value and its speed of rotation varies with the motor speed, its electrical output will vary according to the motor speed. Hence. the excitation of the voltage field winding CVF for the control generator varies according to the speed of the motor IM. The constant voltage generator 2G, as shown, is provided with a single field winding ZGF which is shunt-connected. Any suitable field winding arrangement or control of the field winding arrangement of this generator may be utilized to obtain the desired constant voltage output.

The control generator C is of the self-energizing type. These characteristics are obtained by the use of the series-connected field winding CSF. Winding CSF may be shunt-connected if desired. The adjustable resistor TR is so adjusted in its resistance value that the resistance line of the series field or load circuit is tangent to the initial straight-line portion of the no-load saturation curve of this generator. These characteristics are illustrated graphically in Fig. 5 in which the saturation curve is designated SC, and the resistance line of the load circuit is designated RL. As will be seen from this figure, the resistance line is tangent to the initial portion of the curve as for as the points of tangency T and T. This generator may thus have a voltae output equal to the ordinate of any of the points of tangency of the two curves.

It thereby becomes the function of the voltage and pattern field windings of the control generator to select the proper operating point of this generator along the tangent curves, and to maintain this operating point substantially constant for the particular operating condition.

In this manner, when the pattern and voltage field windings of the control generator are equally energized, the total excitation resulting from these fields is zero, and the electrical output of the control generator at this point is maintained by the self-energizing properties of the machine. Should the voltage field winding CVF drop in its excitation due to a drop in the speed of operation of the motor MI, the pattern field excitation will predominate, and the excitation of this pattern field will be added to that of the self-energizing field to increase the electrical output of the control generator. The motor field winding IMF is thus energized in a higher degree, thus the motor torque and consequently the motor speed are increased. When the speed of the motor increases sufficiently that the excitation of the voltage field winding is equal and opposed to that of the pattern field winding, the selfenergizing properties of the regulating generator maintain the electrical output thereof at this new point. Any departure in speed of the motor at this new operating point will again produce a correction due to the differential action of the pattern and voltage field windings to bring the motor speed to its desired value.

Assuming that the constant current generator IG and constant voltage generator 2G are both running at the constant speed controlled by the prime mover PM, the motor IM can be started by pressing the start push button. This causes the relay R to close its contact members RI, thus connecting the control generator pattern field winding CPF across the constant voltage generator 2G. The contact members R2 shunt the start push button and thus maintain the energizing circuit for the coil of the relay R independent of the position of the start push button. The contact members R3 complete an energizing circuit for the coil of the circuit breaker CB also connected across the constant voltage generator. The contact members R4 partially establish an energizing circuit for the coil of the accelerating relay A. Since the coil of the circuit breaker CB is energized, this breaker closes its contact members CBI to connect the motor field winding IMB across the control generator C. The contact members CB2, which normally shunt the armature of the drive motor I M and its series resistor IR, thus effectively deenergizing the armature winding of this motor, now open, and the constant current output of the generator IG circulates through the armature winding of the drive motor. The drive motor now accelerates with the resistor IR in series therewith. The contact members CB3 in conjunction with the contact members R4 now closed complete the energizing circuit for the coil of the accelerating relay A. The accelerating relay A closes its contact members Al to shunt the starting resistor IR from its series connection with the armature winding of the drive motor. Its contact members A2 which parallel the contact members R3 provide an energizing circuit for the coil of the circuit breaker and also the accelerating relay A which is independent of the relay R. As the motor accelerates, the speed responsive switch S closes its contact members. These contact members s unt the contact members RI and thus provide electrical potential for energizing one of the field windings, means for producing an electrical potential which varies according to the motor speed for energizing the other of said differentially connected field windings, and means including a series connected field winding for the regulating generator and a resistor in series therewith for setting the resistance of the series field circuit such that its resistance line is tangent to the initial straight line portion of the no-load saturation curve of the generator.

4. In an electric drive, the combination of, a motor having an armature winding and a field winding, means for supplying a constant electrical current to the motor armature winding, a generator having an armature winding, a series field winding and a pair of differentially related field windings, circuit means connecting the armature winding and the series field winding of the generator in series with the field winding of the motor, means providing a resistance of the armature circuit of the generator of a value that the slope of the resistance line thereof is substantially tangent to the initial straight line portion of the no-load saturation curve of the generator, means for applying a voltage of con-- stant magnitude to one of said differentially related field windings, and means for applying a voltage varying in magnitude with an operating quantity of the motor to the other of the differentially related field windings.

5. In an electric drive, the combination of, a motor having an armature winding and a field winding, means for supplying a constant electrical current to the motor armature winding, a generator having an armature winding, a series field winding and a pair of differentially related field windings, circuit means connecting the armature winding and the series field winding of the generator in series with the field Winding of the motor, means providing a resistance of the armature circuit of the generator of a value that the slope of the resistance line thereof is substantially tangent to the initial straight line portion of the no-load saturation curve of the generator, means for applying a voltage of constant magnitude to one of said differentially related field windings, and circuit means connecting the other of said difierentially related field windings across the armature terminals of said motor.

6. In an electric drive, the combination of, a motor having an armature winding and a field winding, means for supplying a constant electrical current to the motor armature winding 8. generator having an armature winding, a series field winding and a pair of difierentially related field windings, circuit means connecting the armature winding and the series field winding of the generator in series with the field winding of the motor, means providing a resistance of the armature circuit of the generator of a value that the slope of the resistance line thereof is substantially tangent to the initial straight line portion of the no-load saturation curve of the generator, means for applying a voltage'of constant magnitude to one of said difierentially related field windings, a pilot generator driven by said motor, and circuit means connecting the other of said difierentially related field windings to said pilot generator to be energized thereby.

7. In an electric drive, the combination of, a motor having an armature winding and a field winding, a resistor in series with said armature winding and an accelerating relay for shunting said resistor upon energization of the relay, a.

contactor normally shunting the resistor and for energizing the run relay, normally open con-.. tact means on the run relay for partially establishing an energizing circuit for the accelerating relay, motor speed responsive means for completing the energizing circuit ,for the accelerating relay, normally open contact means on the run relay for energizing said contactor, and means for energizing the other of said differentially related field windings in dependence of the speed of said motor.

GEORGE E. KING.

REFERENCES orrEn The following references. are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,323,741 Watson July 6, 1943 2,361,212

King Oct. 24, 1944 

